I've played the game for some time now and I just finished exploring Hikma Island. I do have some suggestions:
1. Displaying date, time, and prayer status on the HUD would be more convenient, less hassle. Though I'm already fairly happy with checking them in the Journal page.
2. Giving final lines to the NPCs, especially NPCs related to quests. It's funny when NPCs repeat their last spoken lines related to their quests, when the quests have been completed a while ago. Instead of saying their last spoken lines, They can say new lines, whether it's simple greetings, or some trivia about Islam/the game world.
3. Some NPCs may not have the correct lines to the current quest progress. For example: Nasser, the man standing near the locked gate in Sadaqah Town. In the demo I played, he speaks the correct lines depending on the status of the gate. When the gate is still locked, he comments on how the gate is locked. After the gate is opened, he is grateful that the gate is opened. However, in the full game, He always says about the gate being locked, even after I opened the gate and finished all the quests in Salam Island.
4. Dividing the Journal entry into two sections: Active Quests and Finished Quests. After completing a quest, the quest will be written in the Finished Quests. That way, we can review all the quests we have done along the journey.
5. Using the closed chest sprite for the 'ender' chest. I just like seeing it always in its closed state. It looks neat, if it's closed when we approach/leave it.
6. Extra XP/bonus/buff when praying in mosques during/right after the call to prayer. In Islam, praying in mosques on time is encouraged, more satisfying, and gives more reward.